AJAX returning 200 but no response from PHP code

if($_GET['email'] && $_GET['new_email']){
       // tried also header("location: " . WWW . "index.php");
         echo 'hello';
        $p = 5;
       echo $p;

       // wont work if I change GET to POST
    }       

$("#changeE_form").submit(function(e) {

    var url = "<?= WWW ?>email.php"; // the script where you handle the form input.

    $.ajax({
           type: "POST",
           url: url,
           data: $("#changeE_form").serialize(), // serializes the form's elements.
         }).done(function(resp) {
    alert(resp); 
});

    e.preventDefault(); // avoid to execute the actual submit of the form.
});

<form action="<?= WWW ?>email.php" name="changeE_form" id="changeE_form" method="post">

                <input type="email" name="email"  placeholder="Email" required>
                                <input type="email" name="new_email"  placeholder="New Email" required>
                <input type="submit"  value="Change Email">
        </form>